Doesn't surprise me about the Merc. 255 base, bore it i80, put an arm in it, you can get, oh, 302 or 308 cubes......Isky cam, ported and relieved, Kong or Vertex mag, three twos, headers and pipes, they will surprise the snot out of a lot of folks.
Mine is 275...stock Merc crank, 120 over....just so I have room for more.
I think they were still whipping Chevy's regularly until they upped the small bock to 327.